In the manufacture of soap bar compositions, such as toilet soaps, several methods have been employed in forming the bar. One method, for example, involves pouring a molten soap composition into a plate frame or mold and allowing the soap to cool. In another method, one for producing a bar that floats, air is "whipped" into the slightly moist soap composition and it is continuously extruded in the form of a rectangular cross sectional rod or ribbon which is then cut into billets and stamped.
A method which enjoys the most commercial popularity utilizes neat soap as it comes from the production step. It is first mixed with a coloring agent, dried to about an 8-18% moisture content, the dried chips or flakes are passed to a hasher where they are broken up, mixed and finally, extruded in the form of small pellets. The pellets are then passed to another mixer or amalgamator where such ingredients as perfumes, coloring agents, organic liquid additives such as emollients and germicides are added. The added material usually varies from about 1 to 6% of the total ingredients of the composition. The addition of the organic liquid additives acts to plasticize the soap composition by making it softer and more pliable. The amalgamator charge is then fed to a system of screw extruders or plodders which are operated in series to cause intimate mixing and blending of the soap composition. The final extruder produces a continuous rectangularly cross sectioned rod which can be continuously cut into individual billets. Alternate systems have replaced the plodders by a roller-mill for the purpose of mixing and blending the composition and have only one extruder which serves to form the continuous rod of soap composition. The cut billets are then stamped to emboss or deboss the detailed graphics present in the stamped die mold which are to be present in the final soap bar configuration. The stamped billets are then wrapped and packaged and are ready for the consumer.
As stated above, the soap composition which leaves the amalgamator is of a soft and pliable nature. This is a desirable feature for the stamping operation in order that the billet may be free flowing in the die cavity so that it forms the detail graphics present in the die mold. However, this requirement of plasticity is counter to the need for having a hard bar after pressing in order to undergo the subsequent wrapping, packaging, etc. operations without marring. In small scale operations this problem of excessive bar softness has been handled by removing the stamped bars from the line and allowing them to "age" and thereby harden before subsequent operations are carried out. This naturally, is an unacceptable technique wherein a continuous operation is desired and also where minimum handling a processing space is sought.
Modern continuous production lines which wish to alleviate the aging process have installed a conditioning tunnel after the billet cutter and before the stamper in the production line. The rationale behind this is to produce a billet which will be soft enough for stamping yet hard enough to withstand the subsequent operation of wrapping, packaging, etc. The conditioning tunnels which are presently used allow the billet to either age harden or to be subjected to refrigerated air to harden the bar. This technique is undesirable in that it produces a billet which is not easily embossed with the detailed graphics present in the die mold of the stamping process nor is the stamped billet hard enough to undergo subsequent operations without damage.
Thus, the serious quality control problem encountered in modern processing is directed to the deformation and marring of the finished stamped billets due to mechanical action of the wrappers, conveyors, and packers. By making a soap billet hard prior to stamping one does not have a free flowing plastic material which can easily form detailed high quality soap bar materials. Yet, if the soap is allowed to age and become hardened it also becomes more brittle. This brittleness results in fractures in the bar when it is subjected to mechanical impact. Thus, tiny hairline fractures are formed on the bar surface in the stamping operation of hardened soap while white powdery substance forms on the surface of the billet due to the scuffing and banging of the soap by the conveyor system and by the subsequent wrapping and packaging processes.